From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta0.migadu.com (out-62.mta0.migadu.com [91.218.175.62]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3B8B83AAF56 for ; Fri, 18 Sep 2026 02:36:28 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.62 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789698995; cv=none; b=s8Q9PbcbT02huxqWpGDYkn4j2760gvqUZj1kygJQ+E4W9S7o9QEhbzzByGjKzmaRtdebRzQmvnb5GAAw6ZMSvixeiBx6m/FJZWRC6NSqFniQtV/HMVAQAkqU3v3YKtall/iaYaEDMNm5ilFLcHEVLLbzIjIVVCqSKnzWsfuP7WE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789698995; c=relaxed/simple; bh=uokSLb5tIWKs9wmoZjlPpYDU82fxVQpNKwqAQMjHX7s=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=lqW7C1ZhJx6MZ2g9aVVcqNPf8WztV9qMhhUYm8/qM5AEUK9Uahm2B8sGJ+cSDVLnmNjeM8W1EOOkzw6gJqt1NjkpwlR+E7B4foe4pr05yO+owE0gYk6ANMQWs4AzVjxxT/O1QTrPGj8Q2CuQ8x6nC2U++Rdm9lhjunB4nrxdYno= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=QUZwkVhE; arc=none smtp.client-ip=91.218.175.62 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="QUZwkVhE" X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=uokSLb5tIWKs9wmoZjlPpYDU82fxVQpNKwqAQMjHX7s=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1789698982; v=1; x=1790303782; b=QUZwkVhEiApuqFBO2Qf3Sr/p7fX6co8bMIR4oUgIrzHtMdkY9hrcU4Xwy6OgO5607RIDk/bB 6qjBSzNIWGstCwnQKGTcu28ei6A/eIE/F631ACwqzzAqf9w6A04RsJQP1gpP6sBqu0PGdX8OIKs YhqyYcHEEz6kqXiD9SONN6ZM= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id 3b51e68b3c915898; Fri, 18 Sep 2026 02:36:22 +0000 X-Mizu-Trace-ID: 3b51e68b3c915898 X-Migadu-Flow: FLOW_OUT Message-ID: Date: Fri, 18 Sep 2026 10:37:21 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v10 5/6] alloc_tag: skip percpu counter allocation when profiling is disabled To: Suren Baghdasaryan Cc: Luis Chamberlain , Petr Pavlu , Daniel Gomez , Sami Tolvanen , Aaron Tomlin , Kent Overstreet , Andrew Morton , linux-modules@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Sashiko , stable@vger.kernel.org References: <20260915070001.113559-1-hao.ge@linux.dev> <20260915070001.113559-6-hao.ge@linux.dev> Content-Language: en-US From: Hao Ge In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Hi Suren On 2026/9/18 08:53, Suren Baghdasaryan wrote: > On Mon, Sep 14, 2026 at 11:59 PM Hao Ge wrote: >> >> After shutdown_mem_profiling() clears mem_profiling_support, >> needs_section_mem() returns false, so later modules have their codetag >> section placed as regular data and never enter the alloc_tag maple tree. >> codetag_load_module() still called load_module(), which allocated a percpu >> counter for every tag; release_module_tags() could not find these modules >> on unload, so the counters leaked. >> >> Return -EOPNOTSUPP from load_module() when profiling is off: >> codetag_module_init() drops the module's cmod, no counters are allocated >> and the module loads without its tags. codetag_unload_module() now always >> calls free_section_mem(), since a module whose module_load() returned >> -EOPNOTSUPP is not in the idr but may still hold a reserved section. >> >> Reported-by: Sashiko >> Fixes: 4835f747d3ed ("alloc_tag: support for page allocation tag compression") >> Cc: stable@vger.kernel.org >> Suggested-by: Suren Baghdasaryan >> Acked-by: Suren Baghdasaryan > > Yeah, I guess I didn't think about alternatives... > > When mem_profiling_support=false, why can't load_module() skip > allocating percpu counters, zero out the whole area between start_tag > and stop_tag and return 0 as success (mem_profiling_support is not > enabled, so we acted accordingly)? > Module will be added into maple tree and later codetag_unload_module() > will find the module, call release_module_tags() (which is a NOOP > because tag->counter==NULL) and finally call free_section_mem(). This > seems more natural than special-casing with EOPNOTSUPP. WDYT? > I see, but the module would then sit in the idr with NULL-counter tags that become visible to readers which today never expect that state. alloc_tag_top_users calls codetag_next_ct() to find the next codetag and alloc_tag_read() would do per_cpu_ptr(NULL) for each cpu - plain pointer arithmetic onto a wild address, an oops straight out of the OOM report. https://elixir.bootlin.com/linux/v7.3-rc3/source/mm/alloc_tag.c#L503 So if the codetag section within this codetag_type ends up meaningless, is there a reason we still return success? We will still maintain cttype->count and allocate a slot for this module inside mod_idr. I'd rather keep the -EOPNOTSUPP version (your original suggestion), also because the comments in load_module() and codetag_module_init() already document this scenario. WDYT? Thanks Best Regards Hao >> Signed-off-by: Hao Ge >> --- >> lib/codetag.c | 10 ++++++++-- >> mm/alloc_tag.c | 4 ++++ >> 2 files changed, 12 insertions(+), 2 deletions(-) >> >> diff --git a/lib/codetag.c b/lib/codetag.c >> index a9cda4c962a3..a0b600720afc 100644 >> --- a/lib/codetag.c >> +++ b/lib/codetag.c >> @@ -240,7 +240,9 @@ static int codetag_module_init(struct codetag_type *cttype, struct module *mod) >> >> if (err < 0) { >> kfree(cmod); >> - return err; >> + /* -EOPNOTSUPP means we can load the module without its tag. */ >> + if (err != -EOPNOTSUPP) >> + return err; >> } >> >> return 0; >> @@ -388,7 +390,11 @@ void codetag_unload_module(struct module *mod) >> ++cttype->content_id; >> } >> up_write(&cttype->mod_lock); >> - if (found && cttype->desc.free_section_mem) >> + /* >> + * A module whose module_load() returned -EOPNOTSUPP is not >> + * in the idr but may still hold reserved section memory. >> + */ >> + if (cttype->desc.free_section_mem) >> cttype->desc.free_section_mem(mod, true); >> } >> mutex_unlock(&codetag_lock); >> diff --git a/mm/alloc_tag.c b/mm/alloc_tag.c >> index 5836803898ad..1ca0409b492b 100644 >> --- a/mm/alloc_tag.c >> +++ b/mm/alloc_tag.c >> @@ -988,6 +988,10 @@ static int load_module(struct module *mod, struct codetag *start, struct codetag >> struct alloc_tag *stop_tag; >> struct alloc_tag *tag; >> >> + /* Profiling disabled: load the module without its tags. */ >> + if (!mem_profiling_support) >> + return -EOPNOTSUPP; >> + >> /* percpu counters for core allocations are already statically allocated */ >> if (!mod) >> return 0; >> -- >> 2.25.1 >>